1. Field of the Invention
The present invention generally relates to semiconductor laser devices and, more particularly, is directed to a semiconductor laser device in which a semiconductor laser chip is mounted on a semiconductor substrate at one region and a plurality of photo-detecting portions for detecting laser light are formed on the surface of the semiconductor substrate at another region separated from the semiconductor laser chip, where the chip is not mounted. In this application, the direction of the laser light emitted from the semiconductor laser chip and whether or not the luminous intensity distribution of the laser light beam in the plane direction (that is, the surface of the substrate) has a symmetrical property can be measured easily and accurately.
2. Description of the Prior Art
A prior art semiconductor laser device is shown in FIG. 1 in which a monitor photodiode b is formed on a surface of a semiconductor substrate (for example, N.sup.+ type) a and a semiconductor laser chip c is formed on a portion of the semiconductor substrate a near the photodiode b. A manufacturing method for producing a semiconductor laser device, as used by the applicant is shown in FIG. 2. First, as shown in FIG. 2A, a semiconductor wafer a' is treated so as to form a photodiode. A photodiode b is formed on a part of each of the element forming regions d, and a solder layer e for use in laser chip connection is formed on another portion thereof. In FIG. 2A, lines such as f partition or separate adjacent element forming regions such as d, and the element forming regions d are to be diced or separated along lines f. Then, as shown in FIG. 2B, the surface of the semiconductor wafer a' is half-diced or cut along the lines f, thereby forming grooves such as g. Thereafter, as shown in FIG. 2C, a semiconductor laser chip c is positioned on the solder layer e in each of the element forming regions d. The semiconductor wafer a' is then heated in a furnace to about 250.degree. C. to bond all of the semiconductor laser chips c simultaneously. After the electrical characteristic and the optical characteristic are measured, inspected, screened, or the like, the semiconductor wafer a' is separated along grooves g, as shown in FIG. 2D, thereby separating the element forming regions into discrete elements or devices. Thereafter, as shown in FIG. 2E, the element is bonded to a heat sink i which is formed on a surface of a stem, not shown. Next, leads j and j' are attached to the stem, and the semiconductor laser chip c and the electrode of the photodiode b are bonded by wire k to one another, thus practically mounting the semiconductor laser device.
By this prior art manufacturing method, the semiconductor laser chip is connected to the semiconductor substrate in the wafer state rather than in the element or device state. This has the advantage that the semiconductor laser chips can be bonded simultaneously on a vast number of element forming regions on one semiconductor wafer. In addition, where the semiconductor substrate is still in the wafer state, an electrical characteristic such as a threshold current (Ith) etc., can be measured by using a probe or screening therefor can be carried out. Thus, the costs for the bonding of the semiconductor laser device can be decreased as well as the costs for inspection and screening. The previously-described method is highly advantageous from these standpoints.
However, in the prior art, when the semiconductor substrate a is in the wafer state, it is impossible to measure and inspect the direction in which the laser light is emitted from the semiconductor laser chip c and the symmetrical properties of a far field pattern thereof. The displacement of the laser light in the emission direction and the asymmetrical property of its far field pattern are changed relatively easily by the change in position of the semiconductor laser chip c relative to the semiconductor substrate a in the .theta. direction (i.e., the angular displacement of the semiconductor laser chip c). If such positional displacement exceeds a predetermined tolerance, the semiconductor laser device must be regarded as unsatisfactory and removed from the manufacturing process as soon as possible. Unlike the threshold current (Ith) and the like, the emission direction of the laser light and the symmetrical property of its far field pattern cannot be measured and inspected by any method other than a method in which the semiconductor laser device is practically mounted on a container, the laser light is emitted from the semiconductor laser chip and the laser light emitted outside the container is detected by a photosensor. Thus before the semiconductor laser device is practically mounted, the semiconductor laser device in which the symmetrical property of the far field pattern exceeds tolerances cannot be removed from the manufacturing process. With respect to such an unsatisfactory semiconductor laser device, the element or device bonding and the wire bonding to the heat sink i are needlessly carried out. This increases the manufacturing cost of the semiconductor laser device and renders it difficult to decrease the manufacturing cost of the semiconductor laser device.